The kinetics of the α-quartz-coesite transformation was investigated at 4 GPa using both powder and single crystal samples. The results could be analyzed by the Avrami rate equation. Determined exponent n gave values close to 1 for both powder and single crystal experiments. This fact suggests that the growth process is able to control the kinetics. Observations by an optical microscopy in partly transformed single crystals indicate that the coesite phase homogeneously nucleates on the surface of the crystal and grows into the interior. In the case of powder samples, the empirically activation energy of the transformation was determined as 200 (±30) kJ/mol.